The existing optical diffusing film is widely used in an apparatus requiring light source, such as a LCD backlight, an advertising lightbox, a lighting lamp, keys of mobile communication devices, etc., to provide uniform illumination. In recent years, there has been a strong demand for higher performance of the optical diffusing film used in LCD, due to the rapid development of LCD backlight and its wide uses in displays of mobile communication devices, displays of notebook computers, desktop monitors, and large-sized LCD TVs. In particular, the demand is mainly focused on enhancing of luminance and uniformity of illumination.
Usually, the existing optical diffusing films applied to LCD backlight are either organic thin films produced by a stretching technique or a multilayer film produced by a coating method, wherein the coating layer of the multilayer film produced by the coating method contains scattering particles in different particle sizes. FIG. 1 shows the configuration of an optical diffusing film prepared by a conventional coating method, which mainly comprises a transparent substrate 10, a diffusing coating 20, scattering particles 40, an antiblocking coating 30 and antiblocking particles 50. The scattering particles 40 having different particle sizes are randomly distributed in the coating of the optical diffusing film produced by the conventional coating method. Incident light which incidents into the coating is sufficiently diffused mainly by the randomly distributed scattering particles 40, such that the direction of the emergent light can be randomly distributed, thereby the defect of the uneven field of the incident light is diminished and flaws of elements of the backlight module underlying the optical film are shielded. Meanwhile, some scattering particles 40 which have larger particle sizes protrude from the surface of the diffusing coating 20, and therefore a curved surface 21 exhibiting certain light-converging ability is formed; accordingly, this optical diffusing film exhibits light-converging ability to some extent. However, it is found that in the configuration of the afore-said film, not only the amount of the scattering particles 40 protruding from the diffusing coating 20 is few, but also the ratio between the thickness of the diffusing coating 20 and the largest particle size of the scattering particles 40 is greater, and the coating density of the scattering particle 40 is smaller. Thus, there is a problem in the afore-said film that, the light-converging ability and the shielding ability is limited.